Novel defects in Al–Pd–Fe complex metallic alloys: A micromechanical modelling approach

Transmission electron microscopy investigations have revealed that in the face centred complex metallic alloy of C₂–Al–Pd–Fe, the dislocations mediating plastic flow are decorated by localized regions of body centred structure in the compressive part of their strain field thus forming composite defects. We calculated the properties of these defects using a micromechanical model. The Eshelby method was employed to estimate the energies involved in the formation of such defects in the face-centred C₂ phase. We could reproduce the experimentally observed features of the defects in terms of their size and spatial configuration. The model describes a unique mechanism of a non-equilibrium defect, i.e., a dislocation, being stabilized by the formation and interaction with another non-equilibrium defect, i.e., a nanometre sized inclusion of different structure.     

Assessment of Nutritional and Antioxidant Potential of Selected Vitality Strengthening Himalayan Medicinal Plants

Three Himalayan medicinal plants (Habenaria intermedia, H. edgeworthii, and Roscoea procera), widely used in vitality strengthening Ayurvedic formulations in India, were assessed for nutritional phytochemical constituents, and antioxidant activity. These target species emerged as a good source of minerals and possessed important micro elements. Individually, H. intermedia contained a high content of total phenols, thiamins, tannins, and calcium; R. procera was rich in potassium and iron content; and H. edgeworthii emerged as a good source of sodium. While various antioxidant assays provided evidences on the antioxidant potential of target species, greater antioxidant potential of H. intermedia as compared to the other two species was revealing. This study, therefore, highlighted the possibilities of harnessing nutritional and antioxidant potential of these species.     

Phonon dynamics of plutonium chalcogenides and pnictides

We have investigated the phonon dynamics of the plutonium compounds (PuX; X = S, Se, Te, As, and Sb) by using rigid ion (RIM) and breathing shell models (BSM), later includes breathing motion of the electrons of the Pu-atoms due to f-d hybridization. We discuss the significance of these two approaches in predicting the phonon dispersion curves of PuX compounds and examine the role of electron-phonon interactions. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report the one phonon density of states and first time calculated the lattice specific heat for these compounds.     

Water absorption of wood polypropylene composite sheet piles and its influence on mechanical properties

The water absorption behavior and durability of extruded wood polypropylene composite (WPC) material used in Z-section sheet piles was investigated. An experimental technique to determine percentage water absorption and its effect on mechanical properties was implemented. Water absorption tests were carried out on specimens cut from flanges and webs of the Z-section by immersion in tap water at 21, 45 and 70 °C. Freeze–thaw resistance of saturated composites was studied by cycling temperatures in the range of 21 to ?29 °C. The absorption behavior followed the kinetics of a Fickian diffusion process. This behavior was modeled using an analytical solution based on Fick’s second law of diffusion. Quasi-static bending tests were conducted periodically on specimens immersed in water to assess degradation in flexural properties. A significant decrease in mechanical properties of the water-saturated specimens compared to the dry control was observed. Degradation of flexural modulus was found to be a strong function of water absorption with initial decrement as percentage water absorption increased and finally stabilized as the absorption process approached saturation. However, freeze–thaw cycling did not have any significant effect on mechanical properties of saturated composites. A phenomenological model for moisture intrusion and its effect on mechanical properties was implemented and applied to explain the experimental findings.     

Steady-state creep of orthotropic rotating disks of variable thickness

Creep analysis of orthotropic rotating disks with variable thickness has been carried out for secondary stage of creep. Norton's power law of creep is employed to derive general expressions for stresses and strain rates in the disks. These expressions have been utilized to find stress and strain rate distributions for disks with the following types of thicknesses - (i) constant thickness, (ii) linearly varying thickness, and (iii) hyperbolically varying thickness. The numerical computations to study the effects of anisotropy and the profile of the disks on stresses and strains have been carried out employing the method of successive approximations. Five different cases of anisotropy have been considered. Selecting a certain type of material anisotropy and an optimum profile for the disk may result in a better design for the turbine disks.     

Thermally-stimulated spontaneous currents from metal-iodine doped polyvinyl pyrrolidone-metal system

A study of the spontaneous response currents from the metal-iodine doped polyvinyl pyrrolidone-metal (MPM) systems, on thermal stimulation at a constant rate, has been made with similar (Al-Al, Ag-Ag and Au-Au) and dissimilar (Al-Cu/Ag/Ni/PbZn) electrode systems. Thermograms of spontaneous current emission of iodine-doped PVP films exhibit two maxima around 90 ± 10°C and 130–160°C in the first heating run, whereas with the second heating run a single peak is found around 140–170°C. The magnitude and direction of current depend on the choice and combination of electrode materials. The position of the current peak in the thermal spectrum shifts with different heating run. A temperature dependence of open-circuit voltage (OCV) is also reported and it was found that OCV varied linearly with the difference in electrode work functions. The active centres of PVP are the carbonyl group of double-bond tertiary nitrogen atom (> N-C=O), and thus the charge transfer complexes are formed with iodine in PVP. The spontaneously-generated current is discussed in terms of weak complex formation with the water molecules and the liberation of different types of charges.     

Evaluation of error probabilities in the presence of timing errors and fading

Using the approximate Fourier series technique we obtain expressions for the probability of error for bandlimited BPSK signalling in the presence of timing errors and fading. The derived results can be used to compute the error probabilities to any desired accuracy for Nakagami-m and Weibull fading channels. The effect of timing error on the performance of the raised cosine pulse has been evaluated for several fading parameters. We also compare the performance of some useful Nyquist pulses known     

Design and development of long-period grating sensors for temperature monitoring

Long Period Gratings (LPGs) have been developed using carbon dioxide laser in a standard optical fibre. LPGs with a periodicity of 600 μm and grating length of 24 mm have been inscribed on standard single mode fibre. Such gratings have been used in designing temperature sensors and temperature is monitored up to 80°C. The sensitivity of such type of sensor is 0·06 nm/°C where as for standard Fibre Bragg Grating (FBG) it is 0·011 nm/°C. The LPG performance is also evaluated after γ-ray irradiation for total dose of 5 KGy and has not shown any effect on transmission spectrum.     

A Technology‐Enhanced Learning Environment for an Optical Fiber Communications Course*

This paper describes a technology‐enhanced learning environment for an undergraduate course on Optical Fiber Communications ( http:ctle.colorado.edunsf2000 ).